Autosomal Dominant Polycystic Kidney Disease (ADPKD) affects 1 in every 400 to 1000 individuals and is one of the most common genetic disorders. Mutations in two integral membrane proteins, PKD1 and TRPP2, are responsible for almost all clinically identified cases of ADPKD. PKD1 and TRPP2 assemble as a complex and have been proposed to function as a receptor protein and a non-selectivecation channel respectively. The molecular mechanism of the function and regulation of the TRPP2 channel and the TRPP2/PKD1 complex and their roles in ADPKD are still largely unknown. One of the main obstacles is the lack of a reliable way to activate the TRPP2 channel. In previous studies, we have made significant contributions toward understanding the molecular basis of this disease by demonstrating a novel 3(TRPP2): 1(PKD1) stoichiometry of the complex and the structure and molecular basis of this stoichiometry. Our long-term goal is to understand the molecular and cellular mechanisms of the assembly, function and regulation of the TRPP2 channel and TRPP2/PKD1 complex, as well as their role in ADPKD. The proposed research is built on the finding in our preliminary study that a single amino acid substitution in TRPP2 causes the channel to be constitutively open. The objective of this proposal is to characterize this gain-of-function (GOF) TRPP2 channel and use it to study the function and regulation of the TRPP2 channel and its role in ADPKD. The main hypothesis is that characterizing the function and regulation of the GOF mutation will lead to a better understanding of the TRPP2 channel and its role in ADPKD. Based on our preliminary data, the project will be pursued in three specific aims. In Aim 1, we will test the hypothesis that the GOF mutant is a good model for TRPP2 study by characterizing its ion channel features and the effects of ADPKD disease- causing mutations. In Aim 2, we will test the hypothesis that extracellular divalent ions block the TRPP2 channel. This blocking is found in our preliminary study and we expect it has important physiological relevance. In Aim 3, we will investigate the rescue of kidney cyst formation in zebrafish embryos by the GOF TRPP2. Knocking down the expression of endogenous TRPP2 or PKD1 in zebrafish embryos causes kidney cysts. Testing the ability of the GOF TRPP2 to rescue this phenotype, especially when PKD1 is absent, will provide new insights into the role of TRPP2 in ADPKD. This research will shed light on the molecular mechanism of TRPP2 channel function and regulation, as well as its role in the disease. It may also lead to the development of new therapeutic strategies. In addition, this AREA award will enhance the research environment at St. John's University by providing numerous opportunities for motivated students to learn the fundamentals of biomedical research.